Our invention relates generally to apparatus for data transfer with disklike record media typically including a flexible magnetic disk, and more particularly to such data transfer apparatus of the type having an index sensor for putting out a series of index pulses representative of the rotational speed of the record medium. Still more particularly, our invention pertains to an electric circuit arrangement, for use in such data transfer apparatus, for ascertaining from the index pulses whether or not the record medium is in constant speed rotation, in the face of invalid pulses that may be generated accidentally by the index sensor.
The flexible magnetic disk, housed in an apertured, protective envelope to make up a disk assembly or cartridge, has usually an index hole defined eccentrically therein, as disclosed for example in Castrodale et al. U.S. Pat. No. 4,089,029. The apparatus for data transfer with the magnetic disk, known also as a disk drive, has an index sensor for optionally sensing the index hole in the magnetic disk during the rotation of the latter. the index sensor puts out an electric index pulse each time it detects the index hole. Among the purposes for which the index pulses are used is the detection of whether or not the magnetic disk is in constant speed rotation and so is ready for the commencement of data transfer. The detection of the disk speed is possible from the repetition rate or spacings of the index pulses. Reference may be had to European Patent Publication No. 123,848, filed by the assignee of our instant application, for more details on this subject.
As heretofore constructed, the disk drive has had a problem in connection with the optical sensing of the index hole in the magnetic disk, possibly resulting in the erroneous or premature determination of the constant speed rotation of the disk.
Let us suppose that, when being loaded in the disk drive the magnetic disk is moved back and forth across the index sensor. Then the index sensor will produce a pulse or pulses just as it does when the index hole travels past the same during the rotation of the magnetic disk. The pulses put out by the index sensor during disk rotation are the valid index pulses whereas those generated as by the mishandling or accidental displacement of the magnetic disk are the invalid pulses that should be suppressed. Conventionally, however, the electronic circuitry of the disk drive has not been equipped to discriminate between the valid and the invalid pulses generated by the index sensor. Thus the conventional disk drive circuitry has been prone to erroneously or prematurely determine the constant speed rotation of the magnetic disk on the basis of the invalid output pulses of the index sensor.
It will be seen that the above described problem is not limited to the flexible magnetic disk drive alone. A similar problem can occur in other comparable devices such as those for use with optical record media.